The recoil properties of the lung and other elastic tissues are due largely to elastic fibers. These complex structures consist of two morphologically distinguishable components; the protein elastin, and 10- 12 nm microfibrils which contain the structural proteins fibrillin, MAGP, and, perhaps, several others. Microfibrils serve to align tropoelastin molecules, the soluble secreted form of elastin, in precise register so that cross-linking regions are juxtaposed prior to oxidation by lysyl oxidase. In the last few years several genetic diseases have been linked to mutations in components of elastic fibers. These include Marfan syndrome which is linked to mutations in fibrillin-1, and supravalvular aortic stenosis (SVAS) which results from mutations in elastin. In both diseases, disorganized elastic fibers lead to alterations in tissue integrity and compromised mechanical function. A similar problem occurs when tissues attempt to repair damage to normal elastic fibers, such as in emphysema, producing new elastin that is disorganized and nonfunctional. Before we can understand abnormal assembly associated with disease, we need to better understand the fundamental principles of normal elastin assembly. This proposal addresses the question of elastic fiber assembly with the following specific aims: 1) To identify how tropoelastin chains align to form the functional, crosslinked polymer. 2) To determine which residues on tropoelastin and MAGP are modified by lysyl oxidase and transglutaminase. 3) To characterize functional domains that mediate interactions between tropoelastin and MAGP. 4) To produce a MAGP-deficient mouse by insertional mutagenesis to determine the role of MAGP in development and elastic fiber assembly. Understanding these basic aspects of elastic fiber assembly will begin to unravel one of the most intractable problems in matrix biology.